In the telecommunications industry and more particularly in the video transmission industry signals (e.g., 5 MHz to 1 GHz) are carried over coax conductors from a headend to customers. At the headend of the systems, numerous signals are manipulated to achieve a wide variety of functions and objectives. For example, signals carried on numerous coax cables may be combined onto a single coax conductor. Similarly, a signal on a main coax conductor may be divided into a plurality of signals carried on branch coax conductors.
FIG. 1 is a top view of a portion of a circuit board having a tuning circuit according to the prior art. A circuit 10 is provided in which tuning coils are used to provide better isolation between ports of a splitter or combiner module. More particularly, the circuit 10 includes a printed circuit board 12, a splitter inductor 14, a first trace 16 and a second trace 18. The first and second trace each have a first end 20, 22 respectively and a second end 21, 23 respectively. The second ends 21, 23 of the first and second traces 16, 18 are coupled together by the splitter inductor 14. While the inductor 14 is referred to as a splitter inductor, the tuning circuit as described could be used in a combiner module. Located at the first ends 20, 22 of the first and second traces 16, 18 respectively, are a first port 25 and a second port 27. If the circuit is being used in a splitter then the first and second ports 25, 27 are output ports. If the circuit is being used in a combiner, then ports 25, 27 are input ports.
Because the first and second traces 16, 18 are physically and electrically connected through the inductor 14, providing isolation between the traces becomes important. It has been found that to provide a better level of isolation between the first and second traces 16, 18, tuning coils 24 and a resistor 29 between the coils were placed on the circuit. In particular, a first via 26 and a second via 28 are provided on the circuit board. Each tuning coil 38 has a first leg 30 and a second leg 32 (see FIG. 2). The first and second legs 30, 32 fit in the first and second vias 32, 34. The tuning coils 24 can then be soldered to the circuit board 12 by any well known method. One tuning coil 24 is placed alongside the first trace 16 and the other tuning coil 24 is placed alongside the second trace 18. Of course, since a splitter or combiner typically would have more than a first and second trace, separate tuning coils would be provided for each trace.
FIG. 2 is a perspective view of the prior art circuit shown in FIG. 1. As can be seen in FIG. 2 each tuning coil 24 has a double loop structure 38. To tune the circuit, a frequency analyzer is coupled to the first and second traces 16, 18 and, while monitoring the frequency response of that portion of the circuit, one adjusts the spacing between each loop by either pressing the loops closer together or pulling them further apart to tune that portion of the circuit.
FIG. 3 is an elevational view of a tuning coil according to the prior art. Such a tuning coil is typically made of copper and more preferably, copper wire having a gauge of 20 AWG. The tuning coil 24 when used in a combiner or splitter might have a length of 1.39 inches, a height of 0.32 inches and a thickness of 0.107 The loop 38 might have a diameter of 0.157 inches. FIG. 4 is a side view of the prior art coil shown in FIG. 3.
While the tuning circuit shown in FIGS. 1-4 provides a degree of isolation, there is always a need to provide for better isolation between traces in a simple and inexpensive way.
According to a first aspect of the invention, there is provided a circuit for providing tuning on a circuit board. The circuit includes a first trace, a second trace and an inductor. The first trace and second trace each have a first end and a second end. The inductor couples the first trace and the second trace at their respective first ends. A first tuning coil and a second tuning coil are provided. The first tuning coil has a first leg and a second leg coupled together by a loop. The first and second legs are coupled to the circuit board alongside the first trace and the loop of the first tuning coil extends partially over the inductor coupling. The second tuning coil has a first leg and a second leg coupled together by a loop. The first and second legs are coupled to the circuit board alongside the second trace and the loop of the second tuning coil extends partially over the inductor coupling.
According to a second aspect of the invention, there is provided a NX1 combiner circuit. The circuit includes N input traces, a first tuning coil and a second tuning coil. The N input traces are on a circuit board and are divided into N/2 pairs and each pair is coupled to a distinct inductor coupling. The first tuning coil has a first leg and a second leg coupled together by a loop. The first and second legs are coupled to the circuit board alongside a first trace of a pair and the loop of the first tuning coil extends partially over the inductor coupling associated with that pair. The second tuning coil has a first leg and a second leg coupled together by a loop. The first and second legs are coupled to the circuit board alongside a second trace of the pair and the loop of the second tuning coil extends partially over the inductor coupling associated with that pair.
According to a third aspect of the invention, there is provided a NX1 splitter circuit. The splitter circuit includes N output traces, a first tuning coil and second tuning coil. The N output traces are on a circuit board and are divided into N/2 pairs and each pair is coupled to a distinct inductor coupling. The first tuning coil has a first leg and a second leg coupled together by a loop. The first and second legs are coupled to the circuit board alongside a first trace of a pair and the loop of the first tuning coil extends partially over the inductor coupling associated with that pair. The second tuning coil has a first leg and a second leg coupled together by a loop. The first and second legs are coupled to the circuit board alongside a second trace of the pair and the loop of the second tuning coil extends partially over the inductor coupling associated with that pair.
According to a fourth aspect of the invention, there is provided a method of tuning a circuit having a first trace having a first end and a second end, a second trace having a first end and a second end, an inductor coupling the first trace and the second trace at their perspective first ends, a first tuning coil having a first leg and a second leg coupled together by a loop wherein the first and second leg are coupled to the circuit board alongside the first trace, and a second tuning coil having a first leg and a second leg coupled together by a loop wherein the first and second legs are coupled to the circuit board alongside the second trace, The method includes the steps of bending the loop of the first tuning coil so that the loop of the first tuning coil extends partially over the inductor coupling, bending the loop of the second tuning coil over the loop of the first tuning coil so that the loop of the second tuning coil extends partially over the inductor coupling and the loop of the first tuning coil, and adjusting the distance between the loop of the first coil and the loop of the second coil until a desired amount of isolation is achieved between the first trace and the second trace.
According to a fifth aspect of the invention, there is provided an apparatus for providing tuning on a circuit board. The apparatus includes a first tuning coil and a second tuning coil. The first tuning coil has a first leg and a second leg coupled together by a loop and the first and second legs are coupled to a circuit board alongside a first trace. The second tuning coil has a first leg and a second leg coupled together by a loop and the first and second legs are coupled to the circuit board alongside a second trace. The loop of the first tuning coil extends partially over an inductor coupling that couples the first and second trace together at one end and the loop of the second tuning coil extends partially over the inductor coupling.
According to a sixth aspect of the invention, there is provided a circuit for providing tuning on a circuit board. The circuit includes a first trace, a second trace, an inductor coupling, a first tuning coil and a second tuning coil. The first and second traces have a first end and a second end. The inductor coupling couples the first trace and the second trace at their respective first ends. The first tuning coil has a first leg and a second leg coupled together by a loop. The first and second legs are coupled to the circuit board and the loop of the first tuning coil extends partially over the inductor coupling. The second tuning coil has a first leg and a second leg coupled together by a loop. The first and second legs are coupled to the circuit board and the loop of the second tuning coil extends partially over the inductor coupling.